The present invention relates to an information reproducing element for transferring information magnetically or thermo-magnetically recorded on an information recording medium, and further to an information reproducing head comprising the information reproducing element, and an information reproducing apparatus and an information reproducing method for reproducing the information transferred onto the information reproducing element.
With a year-by-year increase in recording density of magnetic recording and thermo-magnetic recording, further enhancement of capacity of storage devices has been considered as a more important factor in order to process large data such as images and motion pictures. There are various methods for recording and reproducing information onto and from a recording medium using a magnetic film. For example, in case of a recording medium of magneto-optical disk, information is magnetically recorded, and then a light beam condensed to an extent near the diffraction limit is irradiated onto the medium thereby to detect a change in the magneto-optical effect caused in the magnetic film.
Such magneto-optical recording methods include an optical modulation recording method and a magnetic field modulation recording method. In the optical modulation recording method, first, a light beam is irradiated onto a magneto-optical disk so as to align the direction of magnetization of the magnetic film. Then, the irradiation of the light beam is modulated correspondingly to data to be recorded thereby to form record marks on the magnetic film. In reproduction, a light beam is irradiated thereby to read out a change in the magneto-optical effect in the reflected light. The plan view shape of the record mark formed by the optical modulation recording is a circle in case of pit position recording in which data xe2x80x9c1xe2x80x9d to be recorded corresponds to a record mark. In contrast, the shape is an ellipse in case of edge position recording in which data xe2x80x9c1xe2x80x9d to be recorded corresponds to an edge of a record mark.
In the magnetic field modulation recording method, with irradiating a light beam, a magnetic field applied is modulated correspondingly to data to be recorded thereby to form record marks on the magnetic film. In reproduction, a light beam is irradiated thereby to read out a change in the magneto-optical effect in the reflected light. The record mark formed by the magnetic field modulation recording is smaller than that by the optical modulation recording method, and the plan view thereof has an arrow feather shape.
Reduction in size of record marks formed on magneto-optical disks has caused a problem that a plurality of record marks exists within a beam spot during reproduction, whereby the reflected light suffers from interference, and whereby a sufficient reproduced signal is not obtained. MSR (magnetically induced super resolution) reproduction technology is a known technology for resolving the problem. In this technology, a predetermined region alone within a beam spot is made reproducible using the temperature distribution within the beam spot, whereby a reproduced signal is obtained with a high SN (signal to noise) ratio without influence of the waveform interference. However, even this MSR reproduction has a limit to high density reproduction.
Another known method for resolving the problem of degradation in SN ratio of the reproduced signal due to the occurrence of waveform interference within a beam spot is a PRML (partial-response maximum-likelihood) method. This method is a signal processing method, for equalizing a signal to a known waveform interference type, and then, maximum likelihood detection is carried out. That is, a reproduced signal is obtained from the reflected light suffering from the waveform interference caused by a plurality of record marks. Then, a sample value is detected from the reproduced signal at each channel clock. Finally, the most probable data is reproduced from both the expectation value of the waveform interference and a series of the sample values. This process permits the reproduction of accurate data even from a reproduced signal with a low SN ratio.
However, the waveform interference in a magneto-optical disk is similar to a waveform interference type PR (1, 1) having many low-frequency signal components. In case that record marks formed by high density recording are reproduced by the PRML method, the expectation value in the maximum likelihood detection increases thereby to degrade the amplitude margin, whereby the influence of noise in the low frequency band increases thereby to prevent accurate reproduction. As such, even this PRML method has a limit to high density reproduction.
Further, in case that the PRML method is applied to the MSR reproduction, the signal band is shifted into a higher frequency band by the super resolution effect thereby to permit a higher density reproduction. However, there has been a problem that the substrate causes noise in the low frequency band thereby to prevent the realization of the effect of PRML method.
Meanwhile, a method is known in which a magnetic film having a large magneto-optical effect is used thereby to obtain a large reproduced signal, whereby record marks formed by high density recording are reproduced. For example, in case that information is magnetically recorded onto a magnetic disk, a recording/reproducing magnetic head using small magnetic poles can perform high density recording. However, in reproduction using such a magnetic head, merely a small electromotive force is induced because of the small size of the magnetic poles, thereby causing the problem of degradation in quality of the obtained reproduced signal. In order to resolve the problem, the magnetic flux of the magnetic disk having undergone high density recording is transferred onto a magnetic film having a large magneto-optical effect, and then a laser light is irradiated onto the magnetic film thereby to reproduce a signal from the transferred magnetic flux by using the magneto-optical effect. This approach generates a high quality reproduced signal.
Such a reproducing method is reported in: xe2x80x9cReadout Characteristics of a magneto-optic Readout headxe2x80x9d in Shingaku-gihou MR87-1, the Institute of Electronics, Information and Communication Engineers; and xe2x80x9cReproduction of recorded signals on a hard disk with a magneto-optical transfer (MOT) readout headxe2x80x9d in Proceedings of the 21st Academic Conference of the Magnetics Society of Japan (1997) 5aF-11. However, in a magnetic head used in such a reproducing method, the amplitude of a reproduced signal notably decreases in case of a recording wavelength of 2 xcexcm or below, thereby causing a problem that the high-density recorded information can not be reproduced.
The principal object of the present invention is to provide an information reproducing element which comprises a plurality of transfer portions separated from each other by magnetically insulating regions and is capable of reproducibly transferring information high-density recorded on an information recording medium. A further object of the present invention is to provide an information reproducing head comprising the information reproducing element, and an information reproducing apparatus and an information reproducing method for reproducing the information on the information recording medium by maximum likelihood detection by using the information reproducing head.
An information reproducing element of the present invention which is arranged so as to face an information recording film on which a plurality of record marks are formed in parallel and is for transferring the magnetic flux of the information recording film to be reproduced, comprises a plurality of transferring portions having magnetically insulating regions intervening therebetween in the direction in which the record marks are aligned in parallel.
In the above-mentioned configuration, in another information reproducing element of the present invention, the direction in which the record marks are aligned in parallel is the length direction and/or the width direction of the tracks on the information recording film.
In the above-mentioned configuration, another information reproducing element of the present invention further comprises a transfer reproducing film onto which the transferred magnetic flux is to be reproduced, on the side opposite to the side of the transferring portions facing the information recording film.
In the information reproducing element of the present invention, a plurality of transferring portions are provided with magnetically insulating regions intervening therebetween, a plurality of small record marks are transferred without interfering with each other. Accordingly, record marks which are high-density recorded can be transferred reproducibly. In case that the Faraday effect is used, a reproduced signal is obtained from the light transmitted through the information reproducing element, whereas in case that the Kerr effect is used, a reproduced signal is obtained from the light reflected in the transfer reproducing film onto which the magnetic flux is transferred via the transferring portion. Further, the plurality of transferring portions can simultaneously transfer record marks within the same track, or alternatively, over separate tracks. Furthermore, the plurality of transferring portions can simultaneously transfer a matrix of record marks spreading both within a track and over separate tracks.
In the above-mentioned configuration, another information reproducing element of the present invention further comprises a transfer layering portion in which the transferring portions and the insulating regions are alternatingly layered in the direction in which the record marks are aligned in parallel and which is arranged so as to face one or a plurality of the record marks.
In the information reproducing element of the present invention, when transmitted light is transmitted through the transfer layering portion, the polarization plane is rotated by the transferred magnetic flux. At that time, the transmitted light is transmitted through the transferring portion having the plurality of layers stacked with intervening insulating regions. Accordingly, the magneto-optical effect is amplified thereby to improve SN ratio.
In an information reproducing element which is arranged so as to face an information recording film on which a plurality of record marks are formed in parallel and is for transferring the magnetic flux of the information recording film to be reproduced, comprises: two transferring portions which have a magnetically insulating region intervening therebetween in the direction in which the record marks are aligned in parallel and are arranged on the surface facing the information recording film; and a transfer reproducing surface onto which a light beam for reproducing from the transferred magnetic flux and which is arranged on the other surface; wherein both the dimension of the surface of the transferring portion facing the information recording film and the dimension of the insulating region are generally the same as the reference clock length for record reproduction.
In the information reproducing element of the present invention, the magnetic flux of the information recording film is transferred via the transferring portions, and then a reproduced signal is obtained from the reflected light of the light beam irradiated onto the transfer reproducing surface.
An information reproducing head of the present invention comprises: the information reproducing element having the above-mentioned configuration; and a slider onto which the information reproducing element is attached and which is arranged so as to face an information recording medium having the information recording film.
In the information reproducing head of the present invention, a slider is provided and arranged on an information recording medium so as to float or slide, and an information reproducing element is mounted on the slider, whereby record marks of the information recording medium are transferred.
An information reproducing apparatus of the present invention comprises: a photoelectric converting unit for receiving emitted light from the information reproducing element and detecting a reproduced signal; a sample value detecting unit for obtaining a sample value of waveform interference from the detected reproduced signal; and a maximum-likelihood detecting unit for performing maximum-likelihood detection depending on the waveform interference type of the information reproducing element by using the sample value obtained by the sample value detecting unit.
An information reproducing method of the present invention comprises the steps of irradiating a light beam onto the information reproducing element arranged so as to face an information recording film and detecting a reproduced signal by the magneto-optical effect; obtaining a sample value of waveform interference from the reproduced signal; and reproducing the information by maximum-likelihood detection depending on the waveform interference type of the information reproducing element by using the obtained sample value.
In the information reproducing apparatus and the information reproducing method of the present invention, an existing waveform interference type is generated by a plurality of transferred record marks, and maximum-likelihood detection is applied on the detected reproduced signal, whereby high precision reproduction is achieved even for a reproduced signal having a low SN ratio.